linux-kernel - Re: [RFC 0/5] mm/bpf/perf: Store build id in file object

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Date:   Fri, 3 Feb 2023 11:03:21 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Jiri Olsa <jolsa@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Hao Luo <haoluo@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        bpf <bpf@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
        "linux-perf-use." <linux-perf-users@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [RFC 0/5] mm/bpf/perf: Store build id in file object

On Thu, Feb 02, 2023 at 03:15:39AM -0800, Alexei Starovoitov wrote:
> On Wed, Feb 1, 2023 at 5:57 AM Jiri Olsa <jolsa@...nel.org> wrote:
> >
> > hi,
> > we have a use cases for bpf programs to use binary file's build id.
> >
> > After some attempts to add helpers/kfuncs [1] [2] Andrii had an idea [3]
> > to store build id directly in the file object. That would solve our use
> > case and might be beneficial for other profiling/tracing use cases with
> > bpf programs.
> >
> > This RFC patchset adds new config CONFIG_FILE_BUILD_ID option, which adds
> > build id object pointer to the file object when enabled. The build id is
> > read/populated when the file is mmap-ed.
> >
> > I also added bpf and perf changes that would benefit from this.
> >
> > I'm not sure what's the policy on adding stuff to file object, so apologies
> > if that's out of line. I'm open to any feedback or suggestions if there's
> > better place or way to do this.
> 
> struct file represents all files while build_id is for executables only,
> and not all executables, but those currently running, so
> I think it's cleaner to put it into vm_area_struct.

There can be many vm_area_structs per file, and like for struct file,
there's vm_area_structs for non-executable ranges too.

Given there's only one buildid per file, struct file seems most
appropriate to me.